Amorphous alloy die cast and heat treatment process of the same

ABSTRACT

A heat treatment process for an amorphous alloy die cast comprises: the amorphous alloy die cast is subjected to an aging treatment at a temperature of about 0.5-0.6 Tg, for a time of about 10 minutes to about 24 hours. The amorphous alloy die cast comprises Zr, and is represented by a formula of (Zr 1−x Ti x ) a (Cu 1−y Ni y ) b Al c M d , in which M is selected from the group consisting of: Be, Y, Sc, La, and combinations thereof, 38≦a≦65, 0≦x≦0.45, 0≦y≦0.75, 20≦b≦40, 0≦c≦15, 0≦d≦30, and the sum of a, b, c, and d in atomic percentages equals to 100.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation of International PatentApplication No. PCT/CN2011/077762, filed Jul. 28, 2011, entitled“AMORPHOUS ALLOY DIE CAST AND HEATING PROCESS OF THE SAME”, which claimsthe priority and benefit of Chinese Patent Application No.201010244468.7, filed with the State Intellectual Property Office of theP. R. China on Jul. 29, 2010. The entire content of both applicationsare incorporated herein by reference.

FIELD OF THE PRESENT DISCLOSURE

The present disclosure relates to methods of manufacturing amorphousalloys, more particularly to an amorphous alloy die cast and a heattreatment process of the same.

BACKGROUND

Extensive research and numerous experiments demonstrated that crystalboundaries, dislocations, stacking faults, or other crystal defects donot exist in amorphous alloys. Hence, amorphous alloys possess aplurality of advantageous material properties that crystal metals do nothave, such as better corrosion resistance, higher frictional resistance,and improved magnetic and electric properties. Amorphous alloys arewidely used in electronic, mechanical, chemical, and national defenseindustries.

At present, bulk amorphous alloy, also known as metallic glass, isusually formed by rapid cooling of melted metal alloy to a temperaturebelow the glass transition temperature. It is believed that rapidcooling may prevent the formation and growth of crystal nucleus. Thusthe melted alloy may solidify directly to form amorphous alloy which hasa long range disordered structure. Bulk amorphous alloys usually aremillimeter-sized. Nowadays, bulk amorphous alloys are mainly prepared inresearch laboratories. Amorphous alloys may be prepared by severalprocesses including melting and suction-casting process in an electricalarc furnace, solvent packaging process, water quenching process, orother processes. However, in these processes, preparation of bulkamorphous alloys to achieve desired material properties may requirestringent processing conditions, such as highly purified raw materials,high degree of vacuum, very rapid cooling, etc. These processes may notbe applicable in the manufacturing industry because of their high costsand low efficiencies.

Therefore, large corporations and research institutes are both seekingfor an amorphous alloy preparation process suitable for high volumemanufacturing under normal processing conditions. Die casting is one ofthe most popular methods for preparing amorphous alloys. However,material properties are usually unstable for amorphous alloys preparedby present die castings processing method under current availableconditions. Thus, the applications of amorphous alloys obtained by diecasting are very limited.

Chinese Patent Application Publication No. CN101550521A discloses arare-earth-based bulk amorphous alloy and its composite material. Thecomposite material is obtained based on the bulk amorphous alloy througha heat treatment process. The heat treatment process includes anisothermal annealing of the rare-earth-based bulk amorphous alloy in afurnace at a temperature within the supercooled liquid region (325-650°C.). The process is performed in a 10⁻³ Pa vacuum environment. Thecomposite material prepared thereof has improved thermal stability,higher electrical resistance, good soft magnetic property, and excellentprocessing capability in the supercooled liquid region. However, thisheat treatment process requires relatively high annealing temperature.The temperature required must reside in the supercooled liquid regionand is higher than the glass transition temperature Tg. Hence, theannealing process may cause portion of the amorphous alloy becomecrystallized.

SUMMARY

The present disclosure aims to solve at least one of the foregoingproblems, including the unstable properties of amorphous alloy obtainedby die-casting techniques and complexity associated with known processesof bulk amorphous alloy preparation.

One embodiment of the present disclosure provides a novel heat treatmentprocess of an amorphous alloy die cast. The heat treatment processincludes an aging treatment performed to the amorphous alloy die cast ata temperature of about 0.5 Tg to about 0.6 Tg for a time period of about10 minutes to about 24 hours.

In one embodiment, the amorphous alloy die cast may be prepared by alow-speed die casting process in a vacuum environment. The process isperformed under a pressure of about 50 Pascal (Pa) to about 200 Pa, witha die casting speed of about 3 meter per second (m/s) to about 5 m/s.The amorphous alloy die cast may have a thickness of about 0.5millimeter (mm) to about 2 mm.

In some embodiments, the aging process may be performed in a positivepressure of about 0.1 MPa to about 0.5 MPa.

In some embodiments, the amorphous alloy die cast may have a thicknessof about 1.0 mm to about 1.5 mm. The aging treatment may be performed ata temperature of about 0.53 Tg to about 0.57 Tg, for a time period ofabout 30 minutes to about 60 minutes.

In another embodiment of the present disclosure, a Zirconium (elementZr) based amorphous alloy die cast is provided. The Zirconium basedamorphous alloy die cast may be prepared by the heat treatment processesdescribed above. The Zirconium based amorphous alloy die cast may becomposed of (Zr_(1−x)Ti_(x))_(a)(Cu_(1−y)Ni_(y))_(b)Al_(c)M_(d), whereinM may be selected from the group consisting of Be, Y, Sc, La, andcombinations thereof; and 38≦a≦65, 0≦x≦0.45, 0≦y≦0.75, 20≦b≦40, 0≦c≦15,0≦d≦30; and the sum of a, b, c, and d in atomic percentages equals to100.

In various embodiments, the amorphous alloy die cast obtained by thedisclosed heat treatment process exhibits higher bending resistance anddecreased property instability.

While the amorphous alloys and methods thereof will be described inconnection with various preferred illustrative embodiments, it will beunderstood that it is not intended to limit the amorphous alloy diecasts and methods thereof to those embodiments. On the contrary, it isintended to cover all alternatives, modifications, and equivalents asmay be included within the spirit and scope of the disclosed subjectmatter as defined by the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects and advantages of the present disclosure willbecome apparent and more readily appreciated from the followingdescriptions taken in conjunction with the drawings, in which:

FIG. 1 shows the X-ray Diffraction (XRD) patterns of samples A1, B1, andC1 according to an embodiment of the present disclosure; and

FIG. 2 shows the Differential Scanning calorimetry (DSC) patterns ofsamples A1, B1, and C1 according to an embodiment of the presentdisclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Traditional amorphous alloy die cast is usually not subjected to heattreatment. During the high-pressure, high-speed casting process oftraditional metal alloys such as Aluminum alloys, Zinc alloys, orMagnesium alloys, gas in the die cast mold can be unavoidably trappedinside the die cast and form subsurface porosities. If the die cast issubsequently subjected to a heat treatment process, gas bubbles may beformed at the surface, causing deformation of the die cast. Hence, boththe properties and the appearance of the die cast are negativelyaffected.

In contrast to traditional Aluminum, Zinc, Magnesium or theircombinational alloys, amorphous alloy has a low temperature supercooledliquid region. The disclosed subject matter provides a novel processmethod that utilizes this supercooled liquid region to significantlyreduce the gas trapped in the amorphous alloy comparing to that in thetraditional metal alloys. Specifically, the disclosed subject matterprovides a die casting process that is performed under a vacuum pressureof about 50 Pa to about 200 Pa, and at a low die casting speed of about3 m/s to about 5 m/s. In addition, risk of die cast bubbling during heattreatment may be effectively eliminated if the post die cast heattreatment is performed under atmospheric pressure or positive pressure,i.e., about 0.1 Pa to about 0.5 MPa, in the range of middle to highpressure.

One embodiment of the present disclosure discloses a novel heattreatment process of an amorphous alloy die cast. The heat treatmentprocess comprises two steps.

The first step comprises die casting and molding the amorphous alloy diecast at a pressure of about 50 Pa to about 200 Pa and at a die castingspeed of about 3 m/s to about 5 m/s. The resulted amorphous alloy diecast may have a thickness ranging from about 0.5 mm to about 2 mm, withmost of the die casts having thicknesses ranging from about 1.0 mm toabout 1.5 mm.

The second step comprises performing an aging treatment on the amorphousalloy die cast, at a temperature of about 0.5 Tg to about 0.6 Tg, for atime period of about 10 minutes to about 24 hours. Tg refers to theglass transition temperature measured in Kelvin. A particular Tg of acertain amorphous alloy may be obtained by DSC testing. DSC testing is acurrently known technique. The aging treatment may be performed atatmospheric pressure or positive pressure. In some embodiments, apositive pressure of about 0.1 MPa to about 0.5 MPa is preferred inorder to prohibit gas from diffusing to the surface of the die cast. Insome embodiments, the preferred aging temperature is about 0.53 Tg toabout 0.57 Tg and the preferred aging time period is about 30 minutes toabout 60 minutes for a amorphous alloy die cast with a thickness ofabout 1.0 mm to about 1.5 mm. Corresponding to different thicknesses ofthe die cast, the preferred aging treatment temperature may be increasedor decreased; and the preferred heat treatment time period may beshortened or extended. However, the aging treatment should be keptwithin about 0.5 Tg to about 0.6 Tg range.

In various embodiments of the present disclosure, the amorphous alloydie cast that is subjected to the above disclosed heat treatment processneither crystallizes, nor has gas bubbles at the surface. The die castexhibits improved material properties and enhanced stability. Theseimprovements may be attributed to the following reasons.

First, during the amorphous alloy die cast preparation process, the diecast is cooled off after molding. Cooling rates at different parts ofthe die cast are different. The different cooling rates may cause someweak areas or stress concentration regions. In the present disclosure,the low aging treatment temperature ranging from about 0.5 Tg to about0.6 Tg enables the relaxation and releasing of the concentratedstresses. Hence, the process disclosed in the present disclosureprevents the amorphous alloy die cast from premature fracturing beforethe material's yield point is reached. As a result, the material'sperformance and stability of the die cast are improved.

Second, the amorphous alloy die cast is formed at a vacuum pressure ofabout 50 Pa to about 200 Pa and at a low casting speed of about 3 m/s toabout 5 m/s. Because the amorphous alloy has a high viscosity, theamount of gases trapped within the amorphous alloy die cast is less thanthat in the traditional alloy die casts. During subsequent agingtreatment performed under middle to high pressure (about 0.1 MPa toabout 0.5 MPa), the positive pressure prohibits the trapped gas fromdiffusing to the surface of the amorphous alloy die cast.

Third, when amorphous alloy is rapidly cooled, the microstructure of theamorphous alloy is in a highly disordered and unstable state. While thelow temperature aging treatment may not provide sufficient energy toovercome the energy barrier required for crystallization, it canovercome the metastable energy barrier and enable the transformation ofthe material structure from a high-energy long-range disordered state toa short-range ordered state. Here, the low temperature aging refers toaging treatment performed below the glass transition temperature. Thecurrent disclosure discloses that such a temperature range is from about0.5 Tg to about 0.6 Tg.

After the low temperature aging process, the alloy may become, forexample, pentagonal or dodecagonal quasicrystals, both have short-rangeordered structures. Although the short-range ordered structure cannotgrow to become crystal, (the crystallization process requires re-meltinginto a disordered state), it can enhance the stability of the materialproperties. Referring to FIG. 2, after the aging treatment, the die castexhibits an increased area under the crystallization peak. The increasedarea under the crystallization peak indicates more energy is releasedduring the crystallization and in turn, indicates a more stable crystalstructure and a more stable material property.

Reference will be made in detail to embodiments of the presentdisclosure. The embodiments described herein with reference to drawingsare explanatory, illustrative, and used to generally understand thepresent disclosure. The embodiments shall not be construed to limit thepresent disclosure. The same or similar elements and the elements havingsame or similar functions are denoted by like reference numeralsthroughout the descriptions.

In the two embodiments disclosed, aging treatments were performed on twotypical Zr-based amorphous alloys composed of Zr₅₅Al₁₅Cu₂₅Ni₅ andZr₄₁Ti₁₄Cu₁₅Ni₁₀Be₂₀, respectively. The two amorphous alloys haveexcellent glass forming ability, excellent mechanical properties andbroad supercooled liquid region. Therefore, these two typical Zr-basedalloys are selected to explain the effects of the aging treatment on theamorphous alloys.

In the first embodiment, high purity (purity is greater than 99.0 wt %)Zr, Al, Cu, and Ni with a weight ratio corresponding to the compositionof Zr₅₅Al₁₅Cu₂₅Ni₅ were melted in an electrical arc furnace.Subsequently, a copper mould was used for die casting in the presence ofa protective Argon gas. The die casting was performed in a condition ofa pressure of 150 Pa and a casting speed of 3m/s. Fifteen amorphousalloy die casts were prepared for experimental purposes, each having asize of 80 mm×6 mm×1.5 mm. The fifteen amorphous alloy die casts werelabeled as A1 to A15, and having a composition of Zr₅₅Al₁₅Cu₂₅Ni₅. Theglass transition temperature Tg was determined to be 704K for this typeof alloy by performing a DSC test. The fifteen die casts were dividedinto three groups.

The first group includes A1 to A5, all of which were not subjected toany aging treatments.

The second group includes A6 to A10, each of which was subjected to anaging treatment in a pressure of 0.2 MPa, at a temperature of 0.53 Tg(373K) , for a time period of 1 hour. The resulted die casts werelabeled as B1 to B5.

The third group includes A11 to A15, each of which was subjected to anaging treatment in a pressure of 0.2 MPa, at a temperature of 0.81 Tg(573K) , for a time period of 1 hour. The resulted die casts werelabeled as C1 to C5.

Property Tests

1) Bending Resistance Test

Pursuing to standard bending resistance test disclosed in GB/T14452-93and using a CMT5105 universal material testing machine, the three-pointbending fracturing tests were performed on each of the die casts groupsA1-A5, B1-B5, and C1-C5. The resulted strength values were recorded. Theaverage and variance of the strength values were calculated. All dataare shown in Table 1.

2) XRD (X-Ray Diffraction) Analysis

In order to determine whether the alloy is amorphous, X-ray powderdiffraction analyses were performed on die cast samples A1, B1, and C1.A D-MAX2200PC X-ray powder diffraction instrument was used, and the XRDanalyses were performed under the following conditions: X-ray radiationwas generated by a copper target; the incident wavelength X is 1.54060A;the accelerating voltage is 40 KV; the current is 20 mA; and the scanstep is 0.04° . The XRD results are shown in FIG. 1. It can be seen thatA1 and B1 have amorphous structures and C1 has a crystal structure (thesharp diffraction peaks of C1 indicate a crystal structure).

3) DSC Test

DSC tests were performed on A1, B1, and C1 with a STA409Thermogravimetric and Differential Thermal Analyzer. An 99% pure Al₂O₃crucible was selected. The results are shown in FIG. 2. It can be seenthat Bl, which was subjected to an aging treatment at a temperature of0.53 Tg, exhibits an increased area under the crystal peaks. Theincreased area means a more stable material property.

TABLE 1 Bending Bending Bending Strength Strength Strength Group 1 (MPa)Group 2 (MPa) Group 3 (MPa) A1 1978.15 B1 2695.73 C1 965.02 A2 1645.26B2 2681.6 C2 644.58 A3 1768.73 B3 2282.61 C3 1248.12 A4 1471.5 B42362.84 C4 683.6 A5 2280.92 B5 2482.1 C5 621.37 Average 1828.912 Average2500.976 Average 832.538 Variance 333.7656 Variance 150.1512 Variance219.2256

In the second embodiment, high purity (purity is greater than 99.0wt %)Zr, Ti, Cu, Ni and Be with a weight ratio corresponding to thecomposition of Zr₄₁Ti₁₄Cu₁₅Ni₁₀Be₂₀ were melted in an electrical arcfurnace. Subsequently, a copper mould was used for die casting in thepresence of a protective Argon gas. The die casting was performed undera pressure of 120 Pa and with a casting speed of 4 m/s. Fifteenamorphous alloy die casts were prepared for experimental purposes, eachhaving a size of 80 mm×18 mm×1 mm. The fifteen amorphous alloy die castswere transition temperature Tg was determined to be 662K for this typeof alloy by performing a DSC test. The fifteen die casts were dividedinto three groups.

The first group includes D1 to D5, all of which were not subjected toany aging treatments.

The second group includes D6 to D10, each of which was subjected to anaging treatment in an atmospheric pressure of 0.1 MPa, at a temperatureof 0.57 Tg (377K) , for a time period of 0.5 hour. The resulted diecasts were labeled as E1 to E5.

The third group includes D11 to D15, each of which was subjected to anaging treatment under a pressure of 0.1 MPa, at a temperature of 0.47 Tg(311 K) , for a time period of 0.5 hour. The resulted die casts werelabeled as F1 to F5.

Property Test

Bending resistance strength test was performed on the 3 groups of diecasts.

Pursuing to standard bending resistance test disclosed in GB/T14452-93and using a CMT5105 universal material testing machine, the three-pointbending fracturing tests were performed on each of the die casts groupsD1-D5, E1-E5, and F1-F5. The resulted strength values were recorded. Theaverage and variance of the strength values were calculated. All dataare shown in Table 2.

TABLE 2 Bending Bending Bending Strength Strength Strength Group 1 (MPa)Group 2 (MPa) Group 3 (MPa) D1 2077.9 E1 2321.8 F1 2184.69 D2 1937.27 E22423.4 F2 2023.29 D3 1606.07 E3 2845.43 F3 1721.34 D4 1715.41 E4 2343.16F4 1763.76 D5 1660.24 E5 2275.54 F5 2107.59 Average 1799.378 Average2441.866 Average 1960.134 Variance 338.1664 Variance 161.4256 Variance300.6715

Conclusion of the Experiments

Referring to Table 1, it is shown that die casts B1-B5, which weresubjected to an aging treatment at a temperature of 0.53 Tg, have betterbending resistance and stability in comparison with die casts A1-A5,which were not subjected to aging treatments, and C1-C5, which subjectedto an aging treatment at a temperature of 0.81 Tg. Referring to Table 2,die casts E1-E5 have improved bending resistance and stability, incomparison with die casts D1-D5, which were not subjected to any agingtreatments, and die casts F1-F5, which were subjected to agingtreatments under a temperature of 0.47 Tg.

In this specification, the terms “one embodiment,” “some embodiments,”“exemplary embodiment,” “specific exemplary embodiment,” or “someexemplary embodiments” mean that the described specific characteristics,structures, materials or features based on the underlining embodimentsexist in at least one of the embodiments or exemplary embodiments.However, in this specification, an exemplary description associated withthe above terms does not necessarily mean the same embodiment. Inaddition, the described specific characteristics, structures, materialsor features may be properly combined in one or more embodiments orexemplary embodiments.

Although explanatory embodiments have been shown and described, it wouldbe appreciated by those skilled in the art that changes, alternatives,and modifications all falling into the scope of the claims and theirequivalents may be made in the embodiments without departing from spiritand principles of the present disclosure.

1. A heat treatment process for an amorphous alloy die cast comprising:subjecting the amorphous alloy die cast to an aging treatment at atemperature of about 0.5 Tg to about 0.6 Tg, wherein Tg is a glasstransition temperature of the alloy, and for a time period of about 10minutes to about 24 hours.
 2. The heat treatment process of claim 1,wherein the temperature is about 0.53 Tg to about 0.57 Tg, and the timeperiod is about 30 minutes to about 60 minutes.
 3. The heat treatmentprocess of claim 1, wherein the amorphous alloy die cast is formed by adie casting process in a condition of a pressure of about 50 Pa to about200 Pa and a die casting speed of about 3 m/s to about 5 m/s.
 4. Theheat treatment process of claim 1, wherein the amorphous alloy die casthas a thickness of about 0.5 mm to about 2 mm.
 5. The heat treatmentprocess of claim 1, wherein the amorphous alloy die cast has a thicknessof about 1.0 mm to about 1.5 mm.
 6. The heat treatment process of claim1, wherein the aging treatment is performed under a positive pressure ofabout 0.1 MPa to about 0.5 MPa.
 7. The heat treatment process of any oneof claims 1, 3, 4, and 6, wherein the amorphous alloy die cast comprisesZr, and is represented by a formula of(Zr_(1−x)Ti_(x))_(a)(Cu_(1−y)Ni_(y))_(b)Al_(c)M_(d), wherein M isselected from the group consisting of: Be, Y, Sc, La, and combinationsthereof, “x” is in the range of from 0 to 0.45 in atomic percentage, “y”is in the range of from 0 to 0.75 in atomic percentage, “a” is in therange of from 38 to 65, “b” is in the range of from 20 to 40, “c” is inthe range of from 0 to 15, “d” is in the range of from 0 to 30, and thesum of a, b, c, and d in atomic percentage equals to
 100. 8. Anamorphous alloy die cast, wherein the amorphous alloy die cast comprisesZr and is treated by the heat treatment process described in any one ofclaims 1, 3, 4, and
 6. 9. The amorphous alloy die cast of claim 8,wherein the amorphous alloy die cast is represented by a formula of(Zr_(1−x)Ti_(x))_(a)(Cu_(1−y)Ni_(y))_(b)Al_(c)M_(d), in which M isselected from the group consisting of: Be, Y, Sc, La, and combinationsthereof, “x” is in the range of from 0 to 0.45, “y” is in the range offrom 0 to 0.75, “a” is in the range of from 38 to 65, “b” is in therange of from 20 to 40, “c” is in the range of from 0 to 15, “d” is inthe range of from 0 to 30, and the sum of a, b, c, and d in atomicpercentage equals to
 100. 10. The amorphous alloy die cast of claim 9,wherein the amorphous alloy die cast is represented by a formula ofZr₅₅Al₁₅Cu₂₅Ni₅ or Zr₄₁Ti₁₄Cu₁₅Ni₁₀Be₂₀.
 11. The amorphous alloy diecast of claim 8, wherein the amorphous alloy die cast has a thickness ofabout 0.5 mm to about 2 mm.